1. Field of the Invention
The invention relates to a technology for fabricating a coil unit for a linear motor or a single coil thereof through line material (conductive wire) winding.
2. Description of the Prior Art
Linear motors are simple in structure, low in parts count, and capable of driving their moving bodies linearly even with precision and speed. Accordingly, the linear motors find wide use as linear drive units or positioning devices in any fields such as exposure devices for semiconductor manufacturing and high precision machine tools.
In general, a linear motor is composed of a magnetic pole unit having magnets and a coil unit having coils. Either one of the units is fixed to a base as a fixed body, and the other is coupled to a moving table or the like as a moving body. The magnetic pole unit and the coil unit are opposed to each other with a constant gap therebetween. When magnetic force is created between the two units, this magnetic force functions as thrust to drive the moving body without contact while maintaining the above-mentioned gap.
For one form of the linear motor, a direct-current linear motor of multi-pole/multi-phase type has been disclosed. In this linear motor, a magnet unit is composed of a plurality of N/S poles that are arranged so that adjoining poles have opposite polarities. Moreover, a plurality of single coils are connected to form a single coil unit as a whole.
Each of the single coils constituting the coil unit has the overall shape of a nearly rectangular ring. Among the four sides of this rectangular, the two sides opposed to each other across the traveling direction function as effective conductors which contribute to the thrust production in a moving body of a linear motor. The other two sides make connecting conductors for connecting the effective conductors. The connecting conductors do not particularly contribute to the thrust production in the linear motor.
Suppose that the magnetic flux density acting on the effective conductors is B (T), the current flowing through the effective conductors is I (A), and the length of the effective conductors is L (m). The thrust F (N) of the linear motor is given by F=BIL. Then, assuming that the number of turns of each single coil is n, F is represented as F=BniL. Where i is the per-wire current.
It can be seen from above that at given dimensions or specifications of the component members, the maximization of the thrust F requires that each single coil be increased in the number of turns.
Generally, a wire can be wound a plurality of times to form a coil by using the method of: preparing a so-called xe2x80x9cwinding formerxe2x80x9d consisting of a male piece and a female piece in conformity with the shape of the coil; coupling these pieces to form a space for the wire to be wound on; and winding the wire around the winding former (over and over) sequentially.
For the case of a coil unit for a linear motor, however, the single coils are arranged closely in a traveling direction. This generally requires that each single coil have its connecting conductors bent sharply from the effective conductors. Therefore, the simple method of winding as described above has the problem that the xe2x80x9cbentsxe2x80x9d are extremely hard to form by means of the winding former""s configuration alone.
Now, brief description will be given of a related technology. The description is given by way of example for the sake of a proper understanding of the foregoing problem to be solved by the present invention or the validity of the present invention.
This technology uses a single coil of saddle shape, formed by sharply bending connecting conductors at approximately 90 degrees with respect to effective conductors. Single coils of such saddle shape are closely arranged in order with little gap therebetween. Here, the single coils having their connecting conductors bent to the right with respect to the traveling direction and the single coils having their connecting conductors bent to the left get into between the effective conductors of the other parties each other. The single coils are interconnected, thereby forming a single coil unit for one linear motor.
When the single coils are driven with a three-phase current, currents having 120-degree differences in phase are passed through adjoining single coils to make a U-V-W three-phase coil unit. Each single pole, a constituting unit of a linear motor, is defined as a part from one N/S pole of the magnet array to a next N/S pole. The number of the single coils corresponding thereto is three; or the U, V, and W phases (per pole).
Conventionally available coil units for a linear motor are formed by combining two types of single coils, more specifically, ones having their connecting conductors bent to the right or left with respect to a traveling direction and ones having no bent. It is characteristic of the coil units to be seen the three phases of coils in a cross section perpendicular to the pole pitch direction. In contrast, this coil unit includes a single type of single coils alone, which are simply distributed to either side and combined with each other to form the coil unit. This means a major characteristic that only two phases of single coils appear in that cross section. These single coils or the coil unit successively offers a number of highly beneficial advantages for reasons including the following. That is, the coil unit is formed with the single coil of one type alone; the length Wo of the connecting conductors is made as short as possible with respect to the length of the effective conductors and the effective conductors are arranged with no gap formed therebetween.
Nevertheless, each single coil in this technology is configured so that a pair of connecting conductor bend at approximately 90 degrees xe2x80x9cin the same directionxe2x80x9d with respect to the effective conductors. The single coils of such configuration are extremely hard to fabricate by xe2x80x9cthe method of winding by using a conventional winding former,xe2x80x9d in fact.
Even if managed to wind, it is extremely difficult to secure the wire at a proper winding angle to the winding former in forming each of the pair of connecting conductors. If the winding tension is increased to prevent the production of slack and the like, a desired coil shape cannot be obtained due to accumulated twists. Besides, the wire density (space factor) varies from place to place, resulting in poor magnetic performance. In particular, when the number of turns n of each single coil is increased for the sake of greater thrust, each side of the rectangular becomes greater in cross-sectional area. This eventually precludes the winding itself.
Related technology has also proposed a technology of: xe2x80x9cinitially winding a rectangular wire of in thickness a plurality of times within the same plane to form a rectangular coil sheet; bending a pair of connecting conductors thereof at approximately 90 degrees in the same direction with respect to the effective conductors to form a coil sheet in a U-shape; and preparing a plurality of such U-shaped coil sheets having slight differences in width and bent positions, and laminating the same into one single coil 2.
Nevertheless, there is no denying that the fabrication of a single coil by laminating a plurality of coil sheets having slight differences in width and bent positions is disadvantageous in terms of cost and flexibility for changing design.
The present invention has been achieved in view of the foregoing problems. It is thus an object of the present invention to provide a technology for allowing even a type (form) of a single coil having a pair of connecting conductors bent sharply in the same direction with respect to effective conductors to be fabricated from a single wire through winding, thereby providing a low-cost easy-to-redesign single coil and a coil unit utilizing the same.
The foregoing object of the present invention has been achieved by the provision of a device for winding a single coil of a coil unit for a linear motor, the single coil having a shape of a nearly rectangular ring as a whole, the device comprising: a conductive wire feeding out mechanism for feeding out a conductive wire serving as material for the single coil in a direction of a Z-axis, where a direction for the conductive wire to be fed out is defined as the Z-axis, and axes crossing at right angles within a plane perpendicular to the Z-axis are defined as X- and Y-axes, respectively; a winding former positioned with its center at a point of origin on the X- and Y-axes, the winding former having locks for the conductive wire at positions corresponding to vertices of the rectangle and functioning as a base in winding the conductive wire into a nearly rectangular shape; and a first rotating mechanism and a second rotating mechanism for allowing the winding former to rotate about the X and Y, two axes, respectively. Here, the first and second rotating mechanisms repeat rotating the winding former by 180 degrees about the X-axis and by 180 degrees about the Y-axis alternately so that the single conductive wire fed from the conductive wire feeding out mechanism in the direction of the Z-axis is wound around the winding former while being locked to the locks in succession (a first aspect of the invention).
In the process of development, the present invention has started with a contrivance to the configuration of the winding former, and then taken account of the technique of winding while slightly tilting and returning a winding former during the winding. Nevertheless, in the conventional method of winging a wire around a winding former of predetermined shape over and over basically in xe2x80x9cthe same directionxe2x80x9d (the method for winding a wire by continuously rotating a winding former in one direction about an axis orthogonal to the wire), component forces off the direction of the Z-axis occurred during the winding as the shape of the coil to be wound became deformed, i.e., got off from a simple cylinder. Besides, it was impossible to prevent the component forces from accumulating with winding. Eventually, accumulated twists occurred inevitably with the result of seriously disturbed winding which could not be contained in an intended shape.
Then, the present inventors have made radical reconsideration of the winding method itself and have invented a technology of winding while rotating a winding former within 180 degrees about two axes xe2x80x9calternately.xe2x80x9d
According to this technology, the following beneficial effects are obtained.
(1) In winding whichever effective conductor or whichever connecting conductor, the wire is always locked to one of the locks when wound so as to bend at 90 degrees around the lock. As a result, despite the irregular-shape coil, the wire can be easily wound in order at both the effective conductors and the connecting conductors without increasing the winding tension excessively.
(2) The first and second rotating mechanisms of the apparatus for winding rotate the winding former always in the same direction, while the winding former is thereby reversed with respect to the feeding direction of the wire about the X-axis and the Y-axis alternately. In view of the rotation of the winding former with respect to the wire, the following four modes are repeated:
1) A forward rotation by 180 degrees about an axis parallel to the connecting conductors;
2) A forward rotation by 180 degrees about an axis parallel to the effective conductors;
3) A reverse rotation by 180 degrees about an axis parallel to the connecting conductors; and
4) A reverse rotation by 180 degrees about an axis parallel to the effective conductors.
After a single (one) round of winding, the wire W twisted by the forward rotations is fully restored by the reverse rotations. This precludes torsion accumulation regardless of the number of wind.
(3) In the winding method according to the present invention, the wire is firmly locked to each lock with torsion. Conversely, the torsion occurring at each lock basically concludes near that lock. Therefore, the occurrence of torsion is limited to the vicinities of the locks alone. The result is that the winding of the wire on each side is effected by simply xe2x80x9cextendingxe2x80x9d the wire from one lock to another through rotation about the next axis (the axis orthogonal to the side for the wire to be extended across). Accordingly, new winding is always performed on a plane containing the Z-axis and the effective conductors, or on a plane containing the Z-axis and the connecting conductors, with little production of side force (torsional stress). As a result, the wire between locks suffers little torsional stress. Torsion occurring on a given lock hardly propagates to the next lock.
Besides, even when it propagates slightly, this torsional stress is cancelled by the above-described effect (2) upon the completion of a single round of winding.
Moreover, according to the present invention, design changes to the single coil can be made by simply modifying the size and/or shape of the winding former or the number of turns. This facilitates designing of extreme flexibility as compared to the structure in which a plurality of coil sheets having different sizes are laminated.
Furthermore, according to the present invention, the wire may use one having a circular cross section, or so-called general-purpose wire, as is. This wire is easily obtainable, which allows a further reduction in delivery time and in costs.
In the present invention, the conductive wire feeding out mechanism for feeding the wire to the winding former is not particularly limited to any concrete configuration. The first and second rotating mechanisms are not particularly limited to any concrete drive structures, either. In some cases, these first and second rotating mechanisms may use ones for rotating the winding former manually.
In addition, the winding former is not particularly limited to any concrete configuration, either. For example, this winding former may comprise a first piece and a second piece detachably overlapped crisscross. Here, the first piece is accommodated between the sides to be the effective conductors. The first piece has a pair of first winding parts extended beyond the two sides to be the connecting conductors, and the connecting conductors are wound on the first winding parts, respectively. The second piece is accommodated between the sides to be the connecting conductors. The second piece has a pair of second winding parts extended beyond the two sides to be the effective conductors. The effective conductors are wound on the second winding parts, respectively. Four intersections formed by the first and second pieces overlapped crisscross function as the locks for a wire, respectively. In this configuration, it is possible to obtain a winding former that can favorably achieve the object of the present invention with a simple structure.
When the winding former is configured thus, the first winding parts of the first piece and the second winding parts of the second piece may have flanges for forming the winding of the wire, protruded from the respective ends toward the counter pieces. The result is that the wire is would while guided by the flanges. This facilitates shaping the effective conductors or the connecting conductors into intended cross-sectional shapes.
In addition, the first winding parts of the first piece may be sloped away from the second piece toward ends of the first winding parts. When a plurality of single coils wound by this winding former are arranged to form a coil unit, the space not contributing to producing a thrust can be reduced further. Then, the per-volume thrust of the coil unit can be increased accordingly.
Speeds of rotation of the winding former by the first and second rotating mechanisms are desirably controlled so that feeding out speed or feeding out tension of the conductive wire fed from the conductive wire feeding out mechanism becomes constant. This allows more uniform, less twisted winding.
Here, the conductive wire feeding out mechanism desirably includes a feeding position control mechanism for changing a position for itself to feed out the conductive wire toward the winding former at least along the X-axis, and changes the position to feed out the conductive wire at least along the X-axis in synchronization with the state of rotation of the winding former by the first and second rotating mechanisms. When this control, i.e., the control of changing the wire-feeding position (coordinate) in synchronization with the state of rotation of the winding former is exercised with precision, it becomes possible to wind the wire in order thread by thread as if to form a simple cylindrical coil.
Incidentally, when the modification of the feeding position is exercised in the direction of the X-axis alone, the winding state of the effective conductors can be rendered in order if the effective conductors are wound by the rotation of the winding former about the X-axis. If the modification/control is exercised even in the direction of the Y-axis, the winding state of the connecting conductors also becomes controllable.
Now, the present invention may be viewed in light of xe2x80x9ca method for winding a single coil.xe2x80x9d Specifically, the invention provides a method for winding a single coil of a coil unit for a linear motor, the single coil having a shape of a nearly rectangular ring as a whole, two opposed sides of the rectangle functioning as effective conductors which contribute to producing a thrust in a moving body of a linear motor, the other two opposed sides of the rectangle functioning as connecting conductors for connecting the effective conductors, the method comprising: the step of feeding out a conductive wire serving as material for the single coil in a direction of a Z-axis, a winding former being positioned with its center at a point of origin on X- and Y-axes, the winding former having locks for the conductive wire at positions corresponding to vertices of the rectangle and functioning as a base in winding the conductive wire into the nearly rectangular shape, where a direction for the conductive wire to be fed out is defined as the Z-axis, and axes crossing at right angles within a plane perpendicular to the Z-axis are defined as X- and Y-axes, respectively; the first rotating step of rotating the winding former by 180 degrees about the X-axis while locking a single conductive wire fed in the direction of the Z-axis to one of the locks; the second rotating step of rotating the winding former by 180 degrees about the Y-axis after the conductive wire is rendered lockable to the next lock in the first rotating step; the third rotating step of rotating the winding former by 180 degrees about the X-axis after the conductive wire is rendered lockable to the next lock in the second rotating step; and the fourth rotating step of rotating the winding former by 180 degrees about the Y-axis after the conductive wire is rendered lockable to the next lock in the third rotating step. The first through fourth rotating steps are repeated subsequently to wind the conductive wire around the winding former successively.
According to the present invention, a method for increasing the wire density of the single coil thus wound around the winding former and forming the single coil further may be provided so that a plurality of such single coils can be arranged at a regular pitch more orderly in forming a coil unit. The method comprises the steps of: loading the single coil into a forming tool, and temporarily fastening the forming tool with the single coil wound around the winding former; passing a predetermined current through the conductive wire to cause heat so that the conductive wire rises in temperature until it enters a plastic range; and fastening the forming tool further from the temporarily-fastened state to shape the conductive wire in the plastic range into predetermined configuration.
The present invention may also relate to a method for fabricating a coil unit from single coils shaped thus. More specifically, the method comprises the steps of: cooling the single coil formed, and then removing the forming tool loaded; preparing a plurality of single coils removed of forming tools, loading the same into a forming device for a unit, and fastening the same; connecting the plurality of single coils to each other according to a specification of the coil unit; and fixing the connecting conductors of the individual single coils with an adhesive.
Furthermore, the present invention may relate to a method for shaping the wound single coils and then shaping the coil unit. More specifically, the method comprises the steps of: releasing the single coil from the winding former; preparing a plurality of single coils released from winding formers, loading the same into a first forming device for a unit, and temporarily fastening the same; connecting the plurality of single coils to each other according to a specification of the coil unit; loading the plurality of connected single coils into a second forming device along with the first forming device, and temporarily fastening the same; passing a predetermined current through the conductive wires of the respective single coils to cause heat so that the conductive wires rise in temperature until they enter a plastic range; fastening the first and second forming devices further from the temporarily-fastened state to form the conductive wires in the plastic range into predetermined configuration; and, after the forming, fitting a forming tool for compression.